Level control for vehicles having at least one air spring

ABSTRACT

The invention relates to a level control arrangement for vehicles with at least one air spring by which a vehicle body is cushioned with regard to at least one vehicle axle, having the following characteristics: a compressed air generator, which can be connected to the air spring by means of an air dryer, the compressed air generator can be connected to the atmosphere by a check valve, which opens in the intake direction of the compressed air generator, the air spring, which can be connected to the atmosphere for discharge purposes via the air dryer or a pneumatically controllable directional valve, wherein the pressure of the air spring is applied to a pneumatic control input of the first directional valve via a second controllable directional valve against the force of a reset force that acts on the pneumatic control input, the pneumatic control input of the first directional valve can be connected to the atmosphere, for the purpose of ending a discharge process of the spring, a line with a compressed air accumulator branches off from the supply line of the air spring via a first changeover valve, wherein the compressed air accumulator is connected to the intake side of the compressed air generator via a second changeover valve and a line that is connected to the compressed air path between the check valve and the compressed air generator, and wherein preferably a pneumatically operating pressure controller is contained in this line.

The invention relates to a level control arrangement for vehicles having at least one air spring with the characteristics according to the preamble of Claim 1. It provides for a compressed air generator that can be connected to the air spring by means of an air dryer. The compressed air generator can be connected to the atmosphere by a check valve that opens in the intake direction of the compressed air generator. The air spring can be connected to the atmosphere for discharging via the air dryer and a pneumatically controllable first directional valve, wherein the pressure in the air spring is applied to the pneumatic control input of the first directional valve via a second electrically controllable directional valve against a reset force that acts on the pneumatic control input. The pneumatic control input of the first directional valve can be connected to the atmosphere via a second directional valve in order to end a discharge process of the air spring.

Level control arrangements of the aforementioned kind are known in the art, which use the air from a pressure accumulator for controlling ride height. A compressed air generator fills this pressure accumulator typically to an air pressure of ca. 20 bar. However, for reasons of air spring/vehicle kinematics, only a pressure of ca. 10 bar can be applied to the air springs. The needed operating pressure of the air spring then corresponds to the pressure in the compressed air accumulator, such that a flow from there to the air spring is no longer possible. An unused residual pressure is left behind in the compressed air accumulator. To be able to raise a vehicle in this state, it would be necessary to increase the pressure in the compressed air accumulator or lift the vehicle directly by means of the compressed air generator. Both solutions considerably increase the length of time it takes for a level change of the vehicle in comparison to the direct lifting action by a supply from the compressed air accumulator, a fact that must be evaluated as a disadvantage.

The object underlying the present invention is to provide a level control arrangement of the kind as identified in the introduction that allows for a substantial increase of the lift speeds, accompanied by higher overall effectiveness and better energy efficiency, and that provides for, in as much as possible, uniform power consumption over the complete operating range with regard to the drive motor of the compressed air generator, which is comprised of an electric motor, resulting in a considerably reduced load to the onboard power supply of the vehicle.

The object is achieved with a level control arrangement for vehicles according to the invention by means of the characteristics of Claim 1. It is provided herein that a first line is branched off from a supply line of the air spring via a first changeover valve, such that the compressed air accumulator is connected, via a second changeover valve and a line that is connected to the compressed air path between the check valve and the compressed air generator, to the intake side of the compressed air generator, and such that this line contains a preferably pneumatically operating pressure controller, wherein this pressure controller can be preferably permanently adjusted, or it can be readjusted relative to the system pressure in the supply line of the air spring.

Further advantageous characterizing features of the invention can be derived from the dependent claims. It is particularly advantageous in this context, when the vehicle body can be raised by means of the compressed air generator, such that the second changeover valve is moved from the closed position into the opened position thereof, and that compressed air is removed from the compressed air accumulator by means of the pressure controller that is supplied, with a closed check valve of the intake side of the compressed air generator, wherein the compressed air generator increases the pressure of the compressed air that is, for example, permanently preset, and this compressed air is supplied via the air dryer to the air spring.

The invention further relates to a method for providing a level control having the characteristics as set forth in Claim 8. Advantageous further characteristics of the invention therein, that relate to the method, are set forth in the further dependent method claims.

The invention provides for the possibility of raising a vehicle with at least one air spring, initially by means of compressed air that is taken from the compressed air accumulator. Furthermore, when, for example, the compressed air level of the compressed air accumulator is no longer sufficient, a vehicle can be raised by means of the compressed air generator, wherein said compressed air generator is efficiently preloaded, via the second changeover valve and the pressure controller, to the pressure level that is still available in the compressed air accumulator. This way, upon being switched on, the compressed air generator, that must deliver compressed air of a higher pressure, already starts up with a substantial starting pressure due to the preloading. This helps to visibly increase the lift speeds. Simultaneously, the power consumption of the electric drive motor of the compressed air generator remains almost unchanged over the operating range “lifting with compressed air generator.” In contrast to the known systems, the present apparatus offers higher overall effectiveness and better energy efficiency. Improved noise properties are achieved by a constant speed level of the electric motor that powers the compressed air generator. The constant power consumption is a further advantageous aspect, wherein a lower load to the onboard network of the vehicle is detected. With a corresponding characteristic of the pressure controller, it is possible to track the preload of the performance of the compressor's electric motor. Correspondingly, the compressed air generator operates with a preload that depends on the system pressure across a very wide operating range with optimal pneumatic and electrical effectiveness. Depending on the compressor concept, this characteristic can look as follows: high system pressure=low pressure of the preload or low system pressure=high pressure of the preload, respectively; or, however, high system pressure=high pressure of the preload or low system pressure=low pressure of the preload, respectively.

Further characteristics of the invention, details and advantages can be derived from the following description.

The invention will be explained in further detail below based on the embodiments as depicted in the drawings.

Shows are as follows:

FIG. 1 is a schematic representation of a level control arrangement in a first operating phase;

FIG. 2 is a schematic representation of a level control arrangement in a second operating phase;

FIG. 3 is a schematic representation of a level control arrangement in a third operating phase;

FIG. 4 is a schematic representation of a level control arrangement in a fourth operating phase;

FIG. 5 is a schematic representation of a level control arrangement in a fifth operating phase.

FIGS. 1 to 5 depict a compressed air supply device 10 that is provided, in particular, for vehicles. This compressed air device 10 can be utilized in varied ways in vehicles. In the drawings, the device is only represented in an exemplary manner in the form of a level control arrangement for motor vehicles and will be explained as such in further detail below. It is indicated therein that the compressed air supply device 10 is configured, in particular, for at least one air spring, for a vehicle body, which is not shown in further detail, cushioned with regard to at least one vehicle axle, which is presently not shown. The shown example provides for the use of four air springs; one single air spring 11 is subsequently referred to in place of all remaining three air springs. Each air spring 11 is connected to a pressure line 12 that contains an electrically controllable 2/2 directional valve 13 the control input of which is connected, via a control line 14, to a control device 15.

The pressure line 12 is connected to a pressure line 16 that is shared by all four air springs and serves as a supply line for them.

The compressed air supply device 10 includes a compressed air generator 17 in the form of a compressor that includes a motor/pump unit, which is connected on the intake side with a pressure line 18 that contains a check valve 19 that opens in the suction direction toward the compressed air generator 17 and closes in the opposite direction by means of a spring load. A pressure line 20 is connected to the pressure side of the compressed air generator 17 that contains an air dryer 21 having an output that is, for example, in connection with the pressure line 16 via a choke.

A pressure line 23 branches off from the pressure line 20 at 22 between the compressed air generator 17 and the air dryer 21, which contains a pneumatically controllable 2/2 directional valve 24 and transitions to the atmosphere after this valve 24. In the first switching state of the valve 24 as shown in FIGS. 1, 2, 3 and 5, the pressure line 23 is blocked from the atmosphere. In the second switching state of the valve 24, as shown in FIG. 4, the pressure line 23 is connected to the atmosphere.

A pressure line 26 branches off at 25 in the flow direction downstream of the air dryer 21, which has an electrically controllable 3/2 directional valve 27 disposed therein, by which the pressure line 26 is connected to the pneumatic control input 28 of the directional valve 24. In the first switching state of the electrically controllable directional valve 27 that is shown in FIGS. 1, 2, 3 and 5, the pneumatic control input 28 of the directional valve 24 is connected to the atmosphere by the directional valve 27 via a connection line 29. In the second switching state of the directional valve 27 that is depicted in FIG. 4, the pressure line 26 is, in contrast, switched through such that the pressure line 26 routes the pressure, which is branched off by the pressure line 16 via the branch-off 25, to the pneumatic control input 28, whereby the directional valve 24 is brought into a second switching state thereof, in which, by this valve 24, the pressure line 23 is switched through to the atmosphere. The air pressure can also escape into the atmosphere by means of the air dryer 21, up to the preset pressure level. The air dryer 21 is regenerated during this step. The compressed air generator 17 is without function therein.

A pressure line 31 branches off, upstream of the branch-off of the respective pressure line 12 at the branch-off 30, from the pressure line 16, which is the supply line of the air springs 11, and in which there is disposed a first changeover valve 32 in the form of an electrically controllable 2/2 directional valve. A compressed air accumulator 33 is contained inside this pressure line 31 downstream of the first changeover valve 32. Following the compressed air accumulator 33 is a pressure line 34 that is connected to the pressure line 18 in the area between the check valve 19 and the intake side of the compressed air generator 17. The pressure line 34 contains, downstream of the compressed air accumulator 33 a second changeover valve 35 in the form of an electrically controllable 2/2 directional valve and, additionally, a pressure controller 36. The second changeover valve 35 is, according to FIGS. 1, 2 and 4, in the first switching state in which this valves is closed, which means the pressure controller 36 is without function. On the other hand, in the phase as depicted in FIGS. 3 and 5, the second changeover valve 35 is in the second switching state in which the pressure line 34 is switched through, such that the compressed air accumulator 33 is in connection with the pressure line 18 and the uptake side of the compressed air generator 17 in such a manner, via the pressure line 34, the open second changeover valve 35 and the pressure controller 36, that the compressed air generator 17 is preloaded with pressure from the compressed air accumulator 33, wherein the compressed air generator 17 then increases the pressure that is provided by the pressure controller 36 and supplies, with the directional valve 13 of the air spring 11 in the respective open position thereof, the air spring with the pressure from the compressed air generator 17, via the pressure lines 16 and 12. In both phases according to FIG. 3 and FIG. 5, the compressed air generator 17 is thus functional in supplying the air spring 11. The compressed air generator 17 is preloaded, via the pressure line 34 and the pressure controller 36, by the compressed air accumulator 33.

In the embodiment as depicted in FIGS. 1 to 4, the pressure controller 36 is adjusted to a preset permanent value. In the embodiment according to FIG. 5, on the other hand, the pressure controller 36 is readjusted corresponding to the system pressure in the pressure line 16 of the air spring 11 and connected, to this end, via a line 37 to the pressure line 16 that serves as supply line. The pressure controller 36 preferably operates pneumatically.

FIG. 1 depicts an operating state in which the compressed air accumulator 33 is filled and pressurized by means of the compressed air generator 17. To this end, using the control device 15, the first changeover valve 32 is triggered in the open position; the compressed air generator 17 is also triggered, such that the same goes into operation, taking in air from the atmosphere through check valve 19, and then condensing the air. The condensed air is routed through the pressure line 20 to the air dryer 21, where the condensed air is dehumidified. Via the pressure line 16 and branch-off 30, the compressed air reaches the pressure line 31 and the compressed air accumulator 33, into which the compressed air is transported until the preset pressure level is reached.

FIG. 2 depicts a switching state in which the air spring 11 is supplied with compressed air and the vehicle, which is presently not shown, is raised. This occurs by means of the compressed air that is stored in the compressed air accumulator 33. Deviating from FIG. 1, the compressed air generator 17 is not functional here. The first changeover valve 32 is triggered once again in the open position by the control device 15, wherein the directional valve 13 in the pressure line 12 of the air spring is now also triggered in the open position, such that compressed air that is contained therein can reach the air spring 11, opposite to the charging process of the compressed air accumulator 33, via the first changeover valve 32, the pressure line 16, the pressure line 12 and the open directional valve 13. The air that is stored in the compressed air accumulator 33 is thus routed into the air springs 11 until the preset pressure level is reached.

In the switching state as indicated in FIG. 3, the air spring 11 is also supplied with compressed air resulting in the air spring 11 raising the vehicle. To this end, by means of the control device 15, the first changeover valve 32 is moved to the first switching state, meaning the closed state. The directional valve 13 in the pressure line 12 of the air spring 11 is adjusted to the second switching state in which the directional valve 13 reaches the open state. In addition, the second changeover valve 35 is also transferred from the closed position to the open position thereof.

As a result, compressed air is supplied from the compressed air accumulator 33, via the pressure line 34, the open second changeover valve 35, the pressure controller 36 in the line 34, to the intake side of the compressed air generator 17, and the compressed air generator 17 is preloaded with this compressed air from the compressed air accumulator 33. The compressed air generator 17 is activated and increases the pressure that is provided and permanently adjusted by the pressure controller 36, wherein the check valve 19 is closed on the intake side. The pressure that was increased by the compressed air generator 17 is supplied to the pressure line 16 and from there, via pressure line 12 and the open directional valve 13, to the air spring 11. As a result, the vehicle, which is presently not shown, is raised by means of the compressed air generator 17 with a preload of compressed air that was permanently adjusted by the pressure controller 36. In this context, the compressed air generator 17 must increase the compressed air level, starting from the level of the load of the compressed air accumulator 33 and the preload, only to such an extent as is necessary for raising the vehicle by means of the air spring 11. This allows for substantially increasing the lift speeds. The times needed for level changes are shortened considerably. A residual pressure left behind in the compressed air accumulator 33, which is insufficient for raising the air springs 11 and is normally left behind unused in the compressed air accumulator 33, is thus utilized for preloading the compressed air generator 17.

The switching state as shown in FIG. 4 depicts the lowering action of the vehicle, which is presently not shown, accompanied by a release of the pressure into the atmosphere. The compressed air generator 17 is without function during this step. The control device 15 controls the directional valves 13 of the air springs 11 to take their open position. The first changeover valve 32 and the second changeover valve 35 are in the closed position. The directional valve 27 is adjusted to the second switching state by the control device 15, where the pressure line 26 is switched through in such a way that pressure is applied, via pressure lines 12, 16 and 26, to the pneumatic control input 28 of the first directional valve 24, whereby the first directional valve 24 is moved into the open position in which the pressure line 23 is switched through to the atmosphere. It is possible therein for the applied pressure to escape from the pressure spring 11 via the pressure lines 12, 16 and 23 into the atmosphere. During this, a flow passes through the air dryer 21 in the pressure line 16, whereby the air dryer is regenerated. The compressed air escapes through the air dryer 21 into the atmosphere until the preset pressure level is reached.

The switching state as indicated in FIG. 5 corresponds substantially to the switching state according to FIG. 3, wherein, presently as well, the compressed air generator 17 is preloaded from the compressed air accumulator 33 via the pressure line 34, the second changeover valve 35, the pressure controller 36 and the pressure line 34 that leads to the intake side of the compressed air generator 17. Preloading of the compressed air generator 17 that occurs is dependent on the system pressure therein, which acts on the pressure controller 36 via the line 37. The pressure preload of the compressed air generator 17 depends therein on the system pressure. In this instance as well, the compressed air generator 17 fills the air spring 11, when an accumulator pressure in the compressed air accumulator 33 falls below a value that is no longer sufficient for increasing the pressure in the air spring 11. The intake pressure of the compressed air generator 17 does not correspond to the atmospheric pressure, as is the case with filling the compressed air accumulator 33 according to FIG. 1; instead, the intake pressure is readjusted after the second changeover valve 35 has been opened by the pressure controller 36, analogously to the system pressure at the output of the compressed air generator 17. The arrangement operates with a variable preload of the compressed air generator 17. Advantageously, in the embodiment as depicted in FIG. 5, it is possible to track the preload of the performance characteristic of the compressed air generator 17, particularly of the compressor/electric motor, by a corresponding characteristic of the pressure controller 36. Accordingly, the compressor operates with a system-dependent preload across a very wide operating range with optimal pneumatic and electrical effectiveness. Depending on the compressor concept, this characteristic can look as follows: high system pressure=low pressure of preload or low system pressure=high pressure of preload; or, however, high system pressure=high pressure of preload or low system pressure=low pressure of preload, respectively. Using the described arrangement, it is possible to achieve a substantially higher overall level of effectiveness and energy efficiency. It is also advantageous, when the arrangement is used in the vehicle, that there is a clearly reduced, derivable load on the onboard network with constant power consumption. Improved noise properties are the result of an achievable constant speed level of the compressed air generator 17 (compressor/electric motor). With all that, the arrangement is still simple and cost-effective. In terms of the control engineering, preloading the compressed air generator 17 for raising the vehicle is easily implemented.

It can be ascertained that the first changeover valve 32 can be moved from the closed position thereof to the open position for charging the compressed air accumulator 33 according to FIG. 1 by actuating the control device 15. It can be further ascertained that the first changeover valve 32 can be moved from the closed position thereof to the open position for raising the vehicle body from the compressed air accumulator 33, and the compressed air is routed from the compressed air accumulator 33 to the preset pressure level and/or lift level into the air spring 11.

It can also be ascertained that, in order for the vehicle to be raised by means of the compressed air generator 17, the second changeover valve 35 can be moved from the closed position into the open position, and compressed air is removed from the compressed air accumulator 33 via the changeover valve 35 and the pressure controller 36, which is supplied, with a closed check valve 19, via the pressure line 34 to the intake side of the compressed air generator 17, which is preloaded in this manner. The compressed air generator 17 increases the pressure of the compressed air that is supplied via the air dryer 21 to the air spring 11. This causes an increase in the pressure that is either permanently preset by the pressure controller 36 according to FIG. 3 or that is, by means of the pressure controller 36, variably dependent on the pressure of the air spring 11 according to FIG. 5.

The compressed air supply arrangement, particularly the level control arrangement, operates therein as follows: by means of the compressed air generator 17, the at least one air spring 11 can be filled with compressed air by means of an air dryer 21, the compressed air generator 17 can be connected via a check valve 19, opening in the intake direction of the compressed air generator 17, to the atmosphere, the air spring 11 can be connected to the atmosphere for discharging via the air dryer 21 and via a pneumatically controllable first directional valve 24, wherein the pressure in the air spring 11 is applied to the pneumatic control input 28 of the first directional valve 24 via a second electrically controllable directional valve 27 against a reset force that acts on the pneumatic control input 28, and the pneumatic control input 28 of the first directional valve 24 can be connected, for ending an discharge process of the air spring 11, via the second directional valve 27 to the atmosphere. In this design concept, it is possible to branch off compressed air from the supply line 16 of the air spring 11 via a line 31 with a first changeover valve 32 to a compressed air accumulator 33. The compressed air is supplied from the compressed air accumulator 33, via a line 34 that is connected thereto and a second changeover valve 35, to a line connection 18 between the check valve 19 and the compressed air generator 17 on the intake side of the compressed air generator 17. The pressure of the compressed air is increased by means of the compressed air generator 17, and the compressed air is then supplied to the air spring 11. The pressure in the line is preset by a preferably pneumatically operating pressure controller, wherein the pressure controller 36 is either permanently adjusted according to FIGS. 1 to 4, or the pressure that is provided by the pressure controller 36 is variably dependent on the system pressure in the supply line 16 of the air spring. This way, the pressure controller 36 is connected for the readjustment action, via a line 37, to the supply line 16 of the air spring 11.

According to FIG. 1, the compressed air generator 17 fills the compressed air accumulator 33 by means of the intake of air from the atmosphere through the air dryer 21, and with an open first changeover valve 32. When the vehicle body is to be raised by means of air spring 11 via the compressed air accumulator 33, the compressed air that is stored in the compressed air accumulator 33 is supplied, with an open first changeover valve 32 and an open air spring valve 13 of the air spring 11, via the supply line 16, 12.

However, this is only possible up to a pressure of, for example, 10 bar, even if the pressure accumulator 33 is pressurized by the compressed air generator 17 typically to 20 bar of air pressure. When the compressed air accumulator 33 has been discharged to a level of approximately 10 bar, the needed operating pressure for the air spring 11 has been reached. After that, any lift action by supplying the air spring 11 is no longer possible. In this case, a residual pressure of 10 bar remains in the compressed air accumulator 33. In this case, advantageously, the vehicle is raised by the compressed air generator 17 that is preloaded to the pressure from the compressed air accumulator 33. With opened air spring valve 13, the second changeover valve 35 is opened, and compressed air is discharged from the compressed air accumulator 33 by means of the same, as well as the pressure controller 36. This compressed air is supplied, with the check valve 19 closed, via the line 34 to the intake side of the compressed air generator 17.

The compressed air generator 17 then increases the pressure that is either permanently preset by the pressure controller 36, or the pressure of the compressed air that is variably dependent on the pressure of the air spring 11. This air is supplied to the air spring 11.

The pressure controller 36 is only active when the vehicle body is raised by means of the compressed air generator 17.

The compressed air generator 17 is functional only when pressurizing the compressed air accumulator 33 and/or when raising the vehicle body from the state as preloaded via the compressed air accumulator 33.

No. Designation 10 Compressed air supply arrangement 11 Air spring 12 Pressure line of 11 13 2/2 directional valve of 12 14 Control line 15 Control line 16 Pressure line of 11 17 Compressed air generator 18 Pressure line of 17 19 Check valve in 18 20 Pressure line between 17/21 21 Air dryer 22 Branch-off 23 Pressure line 24 2/2 directional valve, pneumatically controllable (1stdirectional valve) 25 Branch-off 26 Pressure line 27 3/2 directional valve (2nd directional valve) 28 Pneumatic control input of 24 29 Connection line 30 Branch-off 31 Pressure line (compressed air accumulator) 32 1st changeover valve (2/2 directional valve) 33 Compressed air accumulator 34 Pressure line 35 2nd changeover valve (2/2 directional valve) 36 Pressure controller 37 Line of 36/16 

1. A level control arrangement for vehicles with at least one air spring (11), by means of which a vehicle body is cushioned with regard to at least one vehicle axle having the following characteristics: a compressed air generator (17) that can be connected to the air spring (11) via an air dryer (21); the compressed air generator (17) can be connected to the atmosphere via a check valve (19) that opens in the intake direction of the compressed air generator (17); for being discharged, the air spring (11) can be connected to the atmosphere via the air dryer (21) and via a pneumatically controllable first directional valve (24), wherein the pressure of the air spring (11) is applied to the pneumatic control input (28) of the first directional valve (24) via a second electrically controllable directional valve (27) against a reset force that acts on a pneumatic control input (28); to end a discharge process of the air spring (11), the pneumatic control input (28) of the first directional valve (24) can be connected to the atmosphere via the second directional valve (27), characterized in that a line (31) with a compressed air accumulator (33) branches off from the supply line (16) of the air spring (11) via a first changeover valve (32), in that the compressed air accumulator (33) is connected via a second changeover valve (35) and a line (34), which is connected to the compressed air path (18) between the reset valve (19) and the compressed air generator (17), to the intake side of the compressed air generator (17), and in that this line (34) preferably contains a pneumatically operating pressure controller (36).
 2. The level control arrangement according to claim 1, characterized in that the pressure controller (36) is permanently adjusted to a preset value.
 3. The level control arrangement according to claim 1, characterized in that the pressure controller (36) is readjusted in relation to the system pressure in the supply line (16) of the air spring (11).
 4. The level control arrangement according to claim 3, characterized in that the pressure controller (36) is connected for readjustment, via a line (37), to the supply line (16) of the air spring (11).
 5. The level control arrangement according to any one of the claims 1 to 4, characterized in that, for the purpose of pressurizing the compressed air accumulator (33), the first changeover valve (32) of the compressed air accumulator (33) can be moved from the closed position to the open position.
 6. The level control arrangement according to any one of the claims 1 to 5, characterized in that, for the purpose of raising the vehicle body, the first changeover valve (32) of the compressed air accumulator (33) can be moved from the closed position to the open position, and the compressed air from the compressed air accumulator (33) is routed to the air spring (11), until the preset pressure level or lift level, respectively, is reached.
 7. The level control arrangement according to any one of the claims 2 to 6, characterized in that the vehicle body can be raised by means of the compressed air generator (17) in that the second changeover valve (35) is moved from the closed position to the open position thereof, and compressed air is discharged via the same and via the pressure controller (36) from the compressed air accumulator (33), which is supplied, with a closed check valve (19), to the intake side of the compressed air generator (17), wherein the compressed air generator (17) increases the pressure of the compressed air that is permanently preset by the pressure controller (36) or that is variably dependent on the pressure in the supply line (16) of the air spring (11), and which is supplied to the air spring (11) via the air dryer (21).
 8. A method for the level control in vehicles that are equipped with at least one air spring (11) by which a vehicle body is cushioned with regard to at least one vehicle axle having the following characteristics: using the compressed air generator (17), it is possible to fill the at least one air spring (11) via an air dryer (21) with compressed air; the compressed air generator (17) can be connected to the atmosphere via a check valve (19) that opens in the intake direction of the compressed air generator (17); for the purpose of discharging, the air spring (11) can be connected to the atmosphere via the air dryer (21) and via a pneumatically controllable first directional valve (24), wherein the pneumatic control input (28) of the first directional valve (24) is subjected to the pressure in the air spring (11) via a second electrically controllable directional valve (27) against the reset force that acts on the pneumatic input (28); for the purpose of the discharge process of the air spring (11), the pneumatic control input (28) of the first directional valve can be connected to the atmosphere via the second directional valve (27), particularly according to claim 1, characterized in that compressed air from the supply line (16) of the air spring (11) can be branched off via a line (31) with a first changeover valve (32) to a compressed air accumulator (33), in that the compressed air from the compressed air accumulator (33) is supplied via a line (34) connected thereto and a second changeover valve (35) to a line connection (18) between the check valve (19) and the compressed air generator (17) on the intake side of the compressed air generator (17), and in that the pressure of the compressed air is increased by means of the compressed air generator (17) and the same is supplied to the air spring (11), and in that the pressure in the line (34) is preset preferably by a pneumatically operating pressure controller (36).
 9. The method according to claim 8, characterized in that the pressure of the compressed air in the line (34) that acts on the intake side of the compressed air generator (17) is permanently adjusted by the pressure controller (36).
 10. The method according to claim 8, characterized in that the pressure that is provided in the line (34) by the pressure controller (36) is variably dependent on the system pressure in the supply line (16) of the air spring (11).
 11. The method according to claim 10, characterized in that the pressure controller (36) is connected to the supply line (16) of the air spring (11) for readjustment via a line (37).
 12. The method according to any one of claims 8 to 11, characterized in that the compressed air accumulator (33) is filled, with an open first changeover valve (32), by the compressed air generator (17) with an intake of air from the atmosphere.
 13. The method according to any one of claims 8 to 12, characterized in that the vehicle body is raised by means of the air spring (11) via the compressed air accumulator (33), in that the stored compressed air that is accumulated in the compressed air accumulator (33) is supplied, with an open first changeover valve (32) and an open air spring valve (13), via the supply line (16, 12) for the air spring (11).
 14. The method according to any one of claims 8 to 13, characterized in that the vehicle body is raised by means of the air spring (11) via the compressed air generator (17) in that, with an open air spring valve (13), the second changeover valve (35) is opened and compressed air is removed from the compressed air accumulator (33) via the same and the pressure controller (36), and this compressed air is supplied, with a closed check valve (19), to the intake side of the compressed air generator (17), wherein the compressed air generator (17) increases the pressure of the compressed air that is permanently preset by the pressure controller (36) or variably dependent on the pressure in the air spring (11), and this compressed air is supplied to the air spring (11).
 15. The method according to any one of claims 8 to 14, characterized in that the pressure controller (36) is only active for raising the vehicle body via the compressed air generator (17).
 16. The method according to any one of claims 8 to 15, characterized in that the compressed air generator (17) is only functional for charging the compressed air accumulator (33) and/or for raising the vehicle body from the state thereof as preloaded by the compressed air accumulator (33). 